Respiratory therapist Kevin Hamilton would be happy to have fewer patients.

IN CALIFORNIA'S SAN JOAQUIN VALLEY, the orchards bloom in spring, the livestock fatten, and the Sierra Nevada rises in the distance--even though you may not be able to see it. The valley is mostly rural, but it's got big-city problems: The source of a cornucopia of agricultural products, the area has some of the dirtiest air in the country--almost as bad as Los Angeles, worse than Chicago, and perennially receiving low marks on the American Lung Association's national air-quality report card.

Pollution blows in from San Francisco and L.A., spews from oil refineries and diesel trucks, and rises from plowed fields and factory-farm feedlots. All of it stays right in the valley, whose bowl shape effectively traps pollutants.

In Fresno, the valley's biggest city, schools fly color-coded flags to alert students to bad air. With a population of less than 500,000, the city has the state's highest childhood asthma rate. Kevin Hamilton, a respiratory therapist and asthma coordinator for Fresno's Community Medical Centers, has his work cut out for him. "It's not that uncommon here to find someone who is disabled from work with asthma," he says. "When I started in this business in 1978, that was almost unheard of. Now we see it more and more."

Hamilton is not a political junkie by any stretch; he confesses to getting most of his news from The Daily Show With Jon Stewart. But, concerned about poor air quality and its health effects, he began asking questions about six years ago. He learned that many of the region's major polluters--especially developers and agribusiness--had gotten a break from the Clean Air Act decades ago, and by now the loopholes were entrenched. "It seemed ridiculous," Hamilton says. "It was crazy to me that [regulators] could still have jobs."

In 2002, Hamilton and a group of local health professionals calling themselves the Medical Advocates for Healthy Air sued the federal government, demanding proper enforcement of the 1970 clean-air law. "It wasn't something we wanted to do," he notes. "We have perfectly good jobs taking care of patients, and we weren't looking forward to getting involved."

As the news about pollution's effects grows more urgent, however, more health professionals are responding. The American Academy of Pediatrics and the American Nurses Association, for example, are now suing the EPA over mercury regulations they contend will allow "subtle but irreversible" brain damage in fetuses.

Essentially, these health organizations are finding it necessary to force the EPA to do its job. Not long after the Fresno group filed its lawsuit, for example, then-EPA administrator Christine Todd Whitman came to town, Hamilton recalls. "I asked her why a group of practicing clinicians had to take time out to engage in litigation. And she said that there was not the political will to get something done and that they really welcomed litigation as a kick in the butt. I found that infuriating."

Initially, the kick from Hamilton's group got results. In a settlement, the EPA agreed to start requiring air-quality permits from farms in the valley, and the California legislature passed a law erasing the state's own agribusiness loophole. Farms began replacing old, dirty diesel gear with new hybrid machinery, railroad companies bought cleaner locomotives, and developers started talking to environmentalists and doctors about building neighborhoods that encourage walking instead of driving.

Then the clinicians got another lesson in real-world politics. The valley's air-quality district dragged its feet on implementing a plan to enforce air-pollution rules, setting off the threat of another lawsuit in 2005. And last December, the EPA proposed new federal standards for particulate pollution that include a blanket exemption for agricultural sources--exactly the kind of loophole the health workers had sued over to begin with.

"The EPA has been gutted by this administration. We just have to admit that," says David Pepper, who, with Hamilton, was a founding member of the Fresno medical advocates group. But, he adds, the medical profession has barely begun to make its voice heard. "You're seeing employers and large health plans taking an interest because it affects their bottom line." When the healthcare behemoths get involved--as they did with, say, seat belts and motorcycle helmets--politicians just might start paying attention.--Monika Bauerlein